Fiber reinforced cement composite materials using chemically treated fibers with improved dispersibility

ABSTRACT

A fiber-reinforced building material in one embodiment incorporates cellulose fibers that are chemically treated with a dispersant to impart improved dispersibility to the fibers. The fibers are treated with a dispersant which deactivates the hydroxyl sites of the fiber surfaces and in some cases, making the fiber surface more hydrophobic. The dispersant inhibits the hydroxyl groups on the cellulose fiber surface from bonding with hydroxyl groups of other fibers and from bonding with hydroxyl groups of the same fiber, thereby significantly reducing inter-fiber and intra-fiber hydrogen bonding. The treated fibers can be readily dispersed and uniformly distributed throughout a mixture without re-clustering or reclumping once the mechanical mixing action stops. The chemically treated fibers with improved dispersibility improve the fiber distribution and reinforcing efficiency, which in turn improves key physical and mechanical properties of the material such as the modulus of rupture, z-direction tensile strength, and toughness, and surface finishes. With improved fiber reinforcing efficiency, less dosage of fiber is needed to achieve the required physical and mechanical properties.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.09/969,742, filed on Oct. 2, 2001, entitled FIBER CEMENT COMPOSITEMATERIALS USING SIZED CELLULOSE FIBERS. This application also claims thebenefit of U.S. Provisional Application No. 60/274,414, filed on Mar. 9,2001. The entirety of each of these applications is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention in one embodiment relates to the chemical treatment ofcellulose fibers to impart the fiber with improved dispersibility andreinforcing efficiency in fiber reinforced composite materials. Moreparticularly, in one embodiment, this invention relates to cellulosefiber reinforced cement composite materials using chemically treatedfibers with improved dispersibility, including fiber treatment methods,formulations, methods of manufacture and final products with improvedmaterial properties relating to the same.

2. Description of the Related Art

Fiber-reinforced cement products such as building sheets, panels, planksand roofing have been used for building construction for more than onehundred years. Reinforcing fibers used in such building products includeasbestos fibers, cellulose fibers (see, e.g., Australian Patent No.515151, U.S. Pat. No. 6,030,447), metal fibers, glass fibers and othernatural or synthetic fibers. In recent years, the use of asbestos fibershas decreased substantially due to health concerns associated with theexposure and inhalation of asbestos fibers. As a viable alternative,wood cellulose has become one of the predominant fibers used incommercial fiber-reinforced building materials because it is aneffective, low cost, renewable natural reinforcement fiber compatiblewith common fiber cement manufacturing processes, including theautoclave process.

However, cellulose reinforced fiber cement materials can haveperformance drawbacks such as lower reinforcing efficiency, lowerstrength and toughness due to poor fiber dispersion and uneven fiberdistribution in the cement mix. These drawbacks are largely due to thehydrophilic nature of cellulose fibers. It is generally understood thatcellulose fibers are primarily polysaccharides comprised of five or sixcarbon sugars that have multiple hydroxyl and carboxyl functionalgroups. These functional groups provide cellulose fibers with a strongtendency to form hydrogen intra-fiber and inter-fiber bonds. Hydrogenbonding between fibers often results in the formation of fiber clumps orclusters. The fiber clusters are difficult to disperse in a cementitiousmixture even with the help of hydrapulping and refining processes asdescribed in Australian Patent No. 515151. These fiber clusters are evenmore difficult to disperse in dry and semi-dry processes such asextrusion, molding, Magnani and casting. Moreover, hydrogen bondingbetween different hydroxyl groups of the same fiber is likely to promotefiber curling or forming fiber balls, which can also result in lowerfiber reinforcement efficiency.

For example, when the fibers are dried in the process of forming sheets,the hydrogen bonding within and among cellulose molecules issufficiently strong such that complete dispersion or fiberization of thedried fibers by mechanical means is extremely difficult to achieve. Useof poorly dispersed or fiberized fibers in fiber cement compositematerials usually results in uneven fiber distribution and lowerreinforcing efficiency, which in turn can lead to lower strength,toughness, and strain in the final fiber cement product. Thus, in orderto achieve a certain level of reinforcement, substantially more fibersare needed to compensate for the uneven fiber distribution in thecementitious matrix, which in turn can significantly increase thematerial cost.

A number of prior art references disclose methods of improving fiberdispersion in a cementitious mix. However, all of these references aredirected toward using mechanical action to break the bonds betweenfibers. For example, U.S. Pat. No. 3,753,749 to Nutt discloses millingor otherwise mechanically preparing the fibers beforehand so that thefibers can be uniformly distributed in a concrete mix. U.S. Pat. No.5,989,335 to Soroushian discloses using mechanical action to reduce thebonding between fibers so that the fibers can be dispersed inconventional concrete mixes. One disadvantage of using mechanical meansto break the inter-fiber bonding is that once the mechanically dispersedfibers are placed in the concrete mix, hydrogen bonds can again formbetween the fibers and cause the fibers to re-cluster in the mix.

In the paper industry, some research has been directed toward chemicallytreating cellulose fibers to reduce the fiberization energy needed tofiberize the pulp. Since high energy is typically required to fiberizepulp with strong inter-fiber hydrogen bonding, efforts have been made toreduce the hydrogen bonding among fibers in the pulp by adding organicand/or inorganic chemicals called debonders to lower the fiberizationenergy requirement. The debonders are typically surfactants but can alsobe inorganic fillers. These treated fibers have been developed primarilyfor applications in diaper and sanitary napkin manufacturing.

Thus far, these chemically treated fibers have been used exclusively inthe paper industry for the purpose of reducing fiberization energyduring fiberization processes such as hammermilling. There has been nomotivation to use these chemically treated fibers to improve fiberdispersion as fiber dispersion is generally not a concern for thepapermaking industry since the majority of the papermaking processessuch as Fourdrinier, cylinder (Hatschek) and twin-wire use very dilutefiber slurry. The fiber consistencies in these slurries are typicallybetween about 0.01% to 4%. At such low consistencies, water will breakmost of the inter-fiber hydrogen bonds while the remaining fiberclusters can be easily dispersed using mechanical means such ashydrapulping, pumping, deflakering and refining.

Poor fiber dispersion continues to pose a serious problem in themanufacture of fiber reinforced cement composite materials, especiallywhen long fibers are used in a dry or semi-dry process wherein fiberdispersion is even more difficult to achieve. The fiber cement mixturetypically has a solid content of about 30% to 80% by weight in a dry orsemi-dry process such as extrusion, casting or molding processes. Atsuch high solid concentrations, fiber dispersion cannot be achieved bydilution, solvency, or agitation. As a consequence, poorly dispersedfiber bundles or clusters often lead to severe defects in the finalproduct, including a significant loss in mechanical properties. The highalkalinity of the aqueous fiber cement system (pH commonly higher than10, also promotes the hydrogen bonding among fibers, which can make thefibers more difficult to disperse in a cementitious mixture than in mostconventional paper-making systems where the pulp slurry is typicallyunder acidic or neutral conditions.

Accordingly, there is a need for a fiber that can be readily dispersedand uniformly distributed in fiber reinforced composite buildingmaterials. There is also a need for a fiber reinforced building materialhaving improved fiber distribution and reinforcing efficiency, andmaterial formulations and processes for manufacturing the same.

SUMMARY OF THE INVENTION

Certain preferred embodiments of the present invention provide abuilding material incorporating reinforcing fibers wherein at least aportion of the fibers are chemically treated to substantially improvethe dispersibility of the fibers. In one embodiment, the fibers are atleast partially treated with a dispersant so that the fibers can remainsubstantially dispersed in a mixture even after mechanical mixing of thefibers, thereby substantially reducing the occurrence of re-clusteringor clumping of the fibers in the mixture. Preferably, the dispersantbinds hydroxyl groups on the fiber surface so as to substantiallyinhibit bonding between hydroxyl groups of different fibers, therebysubstantially reducing inter-fiber hydrogen bonding. In one embodiment,the dispersant physically blocks the hydroxyl groups so as tosubstantially prevent the hydroxyl groups from bonding with hydroxylgroups of different fibers, and/or of the different sites of the samefiber. In another embodiment, the dispersant comprises at least onefunctional group that chemically bonds to the hydroxyl groups on thefiber surface in a manner so as to substantially prevent the hydroxylgroups from bonding with hydroxyl groups of different fibers and/orother hydroxyl groups of the same fiber. The dispersants can include,but are not limited to, organic and/or inorganic chemicals such assurfactants and debonders that make the fiber surface more hydrophobicand thus more dispersible in an aqueous environment.

One preferred formulation of a building material made in accordance withpreferred embodiments of the present invention comprises a cementitiousbinder, preferably Portland cement; an aggregate, preferably silicawhich may be fine ground if it is to be autoclaved; cellulose fibers, atleast some of the cellulose fibers having surfaces that are at leastpartially treated with a dispersant so as to make the surfaceshydrophobic and the fibers more readily dispersible; and one or moreadditives. In one embodiment, the dispersant comprises a hydrophilicfunctional group and a hydrophobic functional group, wherein thehydrophilic group permanently or temporarily bonds to hydroxyl groups onthe fiber surface in the presence of water or an organic solvent in amanner so as to substantially prevent the hydroxyl groups from bondingwith other hydroxyl groups. The hydrophobic group is positioned on thefiber surface, repelling water and other treated hydrophobic fiberstherefrom. Preferably, the dispersants comprise from about 0.001% to 20%of the oven-dried weight of the fibers. In one embodiment, the cellulosefibers comprise individualized fibers wherein the lignin of the fibersis chemically removed.

A method of manufacturing a fiber reinforced composite building materialusing the formulations described constitutes another embodiment of thepresent invention. One preferred method comprises providing cellulosefibers and treating at least a portion of the cellulose fibers with adispersant. The dispersant physically blocks and/or chemically bonds toat least some of the hydroxyl functional groups on the fiber surface,thereby substantially diminishing inter-fiber hydrogen bonding andmaking the fibers more dispersible in a mixture. In another embodiment,the cellulose fibers comprise chemically treated fluff pulps used in thepaper industry for purposes of reducing the fiberization energy. Thechemically treated fibers have improved dispersibility and are mixedwith a cementitious binder and other ingredients to form a fiber cementmixture. The fiber cement mixture is formed into a fiber cement articleof a pre-selected shape and size. The fiber cement article is cured soas to form the fiber reinforced composite building material.

Some of the above steps can be omitted or additional steps may be used,depending on the particular application. The step of treating the fiberswith a dispersant preferably comprises treating the fibers withinorganic compounds, organic compounds, or combinations thereof usingtechniques involving dry spraying or solution treatment, although othermethods of applying dispersants are feasible, such as coating, andimpregnation. In one embodiment, each of these techniques preferablyoccurs in the presence of water or an organic solvent. Preferably, thestep of mixing the chemically treated fibers with ingredients to form afiber cement mixture comprises mixing the chemically treated fibershaving improved dispersibility with non-cellulose materials such ascementitious binder, aggregate, and additives in accordance withpreferred formulations described herein. In another embodiment, thechemically treated fibers having improved dispersibility can also bemixed with conventional untreated cellulose fibers, fluff fibers, and/ornatural inorganic fibers, and/or synthetic fibers along with otheringredients. The fabrication processes can be any of the existingtechnologies such as extrusion, molding, casting, injection molding,multi-wire forming and Hatschek processing, etc.

Application of the chemically treated fibers of the preferredembodiments improves the fiber dispersion and reinforcing efficiency inthe building material, which in turn improves key mechanical andphysical properties of the material. In one embodiment, incorporation ofthe chemically treated fibers with improved dispersibility in thebuilding material increases the modulus of rupture (MOR) by more thanabout 5%, and/or increases the toughness by at least about 5%, morepreferably by about 20%, and/or increases the strain by more than about5%, and/or increases the z-direction tensile strength by at least about5%, more preferably more than about 10%, when compared with a buildingmaterial made with an equivalent formulation without the chemicallytreated fibers. Moreover, less cellulose fibers may be required inmaking composite materials of substantially the same physical andmechanical properties because chemically treated fibers with improveddispersibility substantially obviate the need to add additional fibersto the cementitious mix to compensate for fiber clumping or clusters.These and other advantages will become more fully apparent from thefollowing description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplifying process flow of one embodiment oftreating fibers with dispersants in solution;

FIG. 2 illustrates exemplifying process flows of several embodiments oftreating fibers with dispersants using a dry spray process;

FIG. 3 illustrates an exemplifying process flow of one embodiment ofmaking fiber reinforced cement composite materials incorporatingchemically treated fibers with improved dispersibility;

FIG. 4 is a graph illustrating key mechanical and physical properties offiber cement building materials made with chemically treated fibers withimproved dispersibility in accordance with one preferred embodiment andfiber cement materials made with conventional untreated fibers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention relate generally tothe chemical treatment of cellulose fibers to impart improved fiberdispersibility and the use of these chemically treated fibers withimproved dispersibility in cementitious fiber reinforced compositebuilding materials. The processing methods of chemically treating thefibers to make them more readily dispersible, formulations of compositematerials using these chemically treated fibers, and improvements in themechanical and physical properties of the final composite material arealso described.

Chemically treated fibers with improved dispersibility are generallydefined to include fibers that can be more readily distributedthroughout a mixture such as a cementitious matrix and remainsubstantially dispersed even after mechanical mixing action stops. Incontrast to fibers that are dispersed primarily by mechanical means,these chemically treated fibers, when incorporated into a mixture,remain substantially dispersed in the mixture without re-clustering orclumping once the mixing action stops.

Fibers with Improved Dispersibility

In one embodiment, this invention relates to the application ofchemically treated fibers with improved dispersibility into cementitiouscellulose fiber reinforced building materials. The chemically treatedfibers generally comprise fibers that are treated with one or morechemical compounds (dispersants) that inhibit the fibers from forminginter-fiber bonds. In one preferred embodiment, the dispersants bind thehydroxyl functional groups on the fiber surface either by physicallyblocking the site or chemically bonding to the hydroxyl groups so as tosubstantially prevent the hydroxyl groups from forming hydrogen bondswith hydroxyl groups on adjacent fibers. The dispersants may be appliedto both long and short cellulose fibers to impart the fibers withimproved dispersibility. Long fiber is herein defined as fibers with alength-weighted average length of longer than about 1 mm, and shortfiber is defined as fibers with length-weighted average length of lessthan about 1 mm. Preferred embodiments of the present invention can beapplied to, but is not limited to, fibers having length-weighted averagelength of about 0.01 to 7.0 mm.

Dispersant Chemicals and Cellulose Fibers for Fiber Treatment

The chemicals selected for improving fiber dispersibility are preferablychemicals that cause the fiber surface to become more hydrophobic and/orcan significantly reduce the occurrence of inter-fiber bonding, thusmaking the fibers substantially more readily dispersible. In oneembodiment, the dispersants attach to the fiber surface in a manner suchthat the dispersants physically block the hydroxyl groups on the fibersurface from contacting adjacent fibers, thereby significantly weakeningthe effects of hydrogen bonding between hydroxyl groups of adjacentfibers. In another embodiment, the dispersants contain functional groupsthat chemically bond to hydroxyl groups on the fiber surface so as toinhibit formation of hydrogen bonding between hydroxyl groups ofdifferent fibers. Chemicals that can be used as dispersants in the fibertreatment process of the preferred embodiments include but are notlimited to:

-   -   polyamine compounds;    -   cationic quaternaryamine compounds including alkyltrimethyl        quaternary ammonium salts, dialkyldimethyl quaternary ammonium        salts, benzylalkyl chlorides, ethoxylated quaternary ammonium        salts, propoxylated quaternary ammonium salts, etc.    -   cationic, anionic, and non-ionic surfactants;    -   combinations of cationic and non-ionic surfactants or of anionic        and non-ionic surfactants;    -   commercially available chemicals that are commonly known in the        paper industry as fluff pulp debonders such as: Berocell 587K,        584, 509, 509HA and 614 from EKA Chemicals Inc. of Marietta,        Ga.; EMCOL CC-42 from Witco Chemicals Inc. of Greenwich, Conn.;        and Quaker 3190 and 2028 from Hercules Inc. of Kalamazoo, Mich.;    -   alkylalkoxylsilane, alkoxylsilane, and halide organosilane.

Additionally, other commercially available chemicals such as surfactantsand debonders can also be applied to the fibers as dispersants in thepreferred fiber treatment process. It will be appreciated that the abovelist of chemical compounds is merely illustrative of examples ofsubstances that can be used to treat the fibers to impart improveddispersibility. The dispersant can also be other suitable organic orinorganic compounds, or combinations thereof, depending on theparticular attributes needed for the specific application of the fibercement material.

Cellulose fibers that are used for chemical treatment with a dispersantcan be made by various pulping methods. In the pulping process, wood orother lignocellulosic raw materials such as kenaf, straw, and bamboo,etc., are reduced to a fibrous mass by the means of rupturing the bondswithin the structures of the lignocellulosic materials. This task can beaccomplished chemically, mechanically, thermally, biologically, or bycombinations of these treatments. Based on the chemicals utilized in theprocess, the chemical pulping methods are classified as Soda, Kraft,Kraft-AQ, Soda-AQ, Oxygen Delignification, Kraft-Oxygen, Solventmethods, and Sulfite pulping, steam explosion or any other pulpingtechniques. In some embodiments, cellulose fibers are separated intoindividual fibers by rupturing the bonds between lignin and cellulosiccomponents. Lignin, which acts as a glue holding cellulose andhemicellulose together to provide mechanical strength in the wood, isbroken and dissolved by chemical reactions. These chemical reactions forindividualizing the fibers can be carried out in a reactor, often calleda digester, under a high temperature around 150 to 250° C. for about 30minutes to 3 hours.

The cellulose fibers used for the dispersant treatment can beunrefined/unfibrillated or refined/fibrillated cellulose pulps fromsources, including but not limited to bleached, unbleached,semi-bleached cellulose pulp produced by various pulping techniques. Thecellulose pulps can be made of softwood, hardwood, agricultural rawmaterials, recycled waste paper or any other form of lignocellulosicmaterials.

Furthermore, the cellulose fibers used can be engineered cellulosefibers such as loaded fibers described in Applicant's copendingapplication entitled FIBER CEMENT COMPOSITE MATERIALS USING CELLULOSEFIBERS LOADED WITH INORGANIC AND/OR ORGANIC SUBSTANCES, U.S. Ser. No.09/969,957, filed on Oct. 2, 2001, and/or sized fibers described inApplicant's copending application entitled FIBER CEMENT COMPOSITEMATERIALS USING SIZED CELLULOSE FIBERS, U.S. Ser. No. 09/969,742, filedon Oct. 2, 2001, and/or biocide treated fibers described in Applicant'scopending application entitled FIBER CEMENT COMPOSITE MATERIALS USINGBIOCIDE TREATED DURABLE CELLULOSE FIBERS, U.S. Ser. No. 09/969,964,filed on Oct. 2, 2001. The entirety of each of these applications ishereby incorporated by reference.

Fiber Treatment

Various methods can be used to treat cellulose fibers with one or moredispersants. A preferred fiber treatment method generally includes thefollowing steps performed in various sequences:

-   -   fiber dispersion/fiberization;    -   fibrillation (mechanical means to increase fiber surface area);    -   fiber conditioning (dewatering, drying or dilution);    -   treatment with one or more dispersants;    -   removal of residual/excessive dispersants; and    -   conditioning of the chemically treated fibers (drying,        humidifying or dispersing).

Some of these steps can be omitted or some other steps may be desirable.The fiber treatment method can be carried out by various means includingbut not limited to treatments in aqueous or organic solvent solutions,and/or treatments by vacuum or pressure spraying of the dispersant ondried or wet cellulose fibers.

Fiber Treatment in Solution

FIG. 1 illustrates an embodiment of a preferred fiber treatment process100 that is carried out in solution. The process 100 begins with step102 in which untreated cellulose fibers are dispersed, fiberized(individualized) and/or fibrillated. The fibers are dispersed at thisstage by mechanically breaking at least some of the inter-fiber bondingto separate the fibers from each other. However, this dispersing step102 typically does not provide the fibers with sufficient dispersibilitysuch that the fibers remain substantially uniformly distributed whenincorporated into a cementitious matrix. At least some of theinter-fiber hydrogen bonds that are broken by mechanical action duringthis dispersing step 102 tend to re-form in a mixture once themechanical mixing action stops, thereby causing the fibers to re-clusteror clump together in the mixture.

Furthermore, individualizing of fibers can occur in a chemical pulpingprocess. Alternatively, it will be appreciated that in performing thispreferred manufacturing process, the chemical pulping step may not benecessary. This is because chemical individualization of fibers is oftendone by the fiber manufacturer, who then provides the fibers to thebuyer on standard lap sheets or rolls. The process 100 can also beapplied to fibers that are not chemically individualized. Thus, in oneembodiment, the individualization of such fibers merely includesmechanically separating the fibers from the sheets or rolls, such as byhammer milling or other methods.

In one embodiment, the untreated cellulose fibers are received in dryform (laps and rolls) or in wet forms (wet laps and in containers).Preferably, the untreated fibers are mechanically dispersed at aconsistency of about 1%-6% to form pulp slurry in a hydrapulper, whichalso imparts some fibrillation. Further fibrillation can be achievedusing a refiner or a series of refiners. Once dispersed, the fibers arethen fibrillated to a range of about 0 to 800 degrees of CanadianStandard Freeness (CSF), more preferably about 100 to 700 degrees ofCSF. Dispersion and fibrillation can be achieved by other techniquessuch as, for example, deflakering, milling, and shredding. However, useof chemically treated fibers without extensive fibrillation is alsoacceptable, or even preferred, for some products and processes.

In the embodiment shown in FIG. 1, subsequent to dispersing the fibersin step 102, the process 100 continues with step 104 in whichfibrillated or unfibrillated fibers in slurry forms are then de-wateredusing press filtration, vacuum filtration or continuous centrifugationto a total solid content of about 2% to 50%. Further de-watering of thefibers can be accomplished by vacuum evaporation drying, flash drying,freeze drying, low temperature oven drying, and other drying techniquesthat do not pose significant damages to the fiber integrity. In oneembodiment, the de-watered fibers are thoroughly mixed in a reactorvessel using dispensers, mixers, or hydra-pulpers of any kind. As shownin FIG. 1, the water from the dewatering step 104 can be recycled to thewater plant 104 a and circulated back to step 102.

The process 100 then follows with step 106 in which dispersant treatmentreactions are carried out. Preferably, prepared dispersants are added tothe reactor while constant agitation and mixing are applied. In oneembodiment, the dispersants comprise surfactants such asquaternaryamine, polyamine, and combinations thereof. Preferably, dosageof the dispersants is up to about 20% of the oven dry mass of thecellulose pulp. Preferably, the dispersants bind the hydroxyl groups onthe fiber surface so as to inhibit the hydroxyl groups from forminghydrogen bonds with hydroxyl groups on adjacent fibers. Weakening ofinter-fiber hydrogen bonding and/or formation of a hydrophobic cloudsurrounding the surfactant treated fibers permit the fibers to becomemore readily dispersible in solution and inhibits the fibers fromclustering once the mechanical mixing action stops. However, the reactorsystems are preferably equipped with some kinds of agitation devices toensure a good mixing.

The dispersant treatment reactions can be carried out in the ambient orat an elevated temperature up to about 250° C., more preferably below150° C. The retention time varies, depending on the particulardispersant, but preferably ranges from about 30 seconds to 24 hours.Batch or continuous reactors of all kinds can be used but continuous orsemi-continuous tank or plug flow reactors are preferred for the fibertreatment in this embodiment.

After a predetermined retention time is reached, the residualdispersants can be separated and removed by centrifugation or filtrationas shown in step 108 of the process 100. In one embodiment, the residualdispersants are recycled and reused. The post reaction fibers arepreferably dried by low temperature oven, vacuum evaporation, and othernondestructive drying techniques. The treated fibers are thenincorporated into fiber cement composite materials in step 110.

TABLE 1 Dispersant Treatment Conditions of Some Embodiments ParametersRanges More Preferable Percent of Fibers in Slurry (% by about 0.01 to70 about 0.5 to 10 weight) Fiber Freeness after Fibrillation about 0 to800 about 100 to 700 (CSF) Dosage of Dispersants (% by fiber about 0.001to 20 about 0.01 to 10 weight)

Table 1 provides examples of reaction conditions of the fiber treatmentprocess 100 described above. However, various changes and modificationsin the conditions can be made from the embodiments presented hereinwithout departing from the spirit of the invention.

Fiber Treatment by Dry Spray

FIG. 2 illustrates several embodiments of treating fibers by dryspraying. The process 200 begins with step 202 in which the rawmaterials are prepared for the treatment. The untreated fibers can bereceived in various forms such as pulp laps (sheets) in bales 202 a;pulp sheets in rolls 202 b; fiberized (hammermill or shredded) fibers inbales, containers, or silos 202 c; fibrillated (refined) dry or semi-dryfibers in bales, silos or containers 202 d; and other dry forms ofcellulose fibers.

As shown in FIG. 2, in the step of treating pulps in forms of rolls orlaps/sheets 202 a and 202 b, dispersants are sprayed onto cellulosefibers as shown in steps 204 a and 204 b. The dispersants may react withmolecules on the fiber surface before, during or after fiberizationprocess. In these spraying systems, the dispersants may be vaporized andthe vaporized chemicals may be pressurized to provide enough sprayingvelocities. Some carrying gases may be used for spraying the dispersantsin latex emulsions. Preferably, the nozzles are selected to generate thefinest spraying particles possible.

In another embodiment of this treatment, dispersants are applied ontopulp laps, rolls or sheets by dipping the pulp webs in solution of thedispersants. After a predetermined retention time to allow dispersantsto react with the fibers, the pulps are then individualized or fiberizedby techniques such as hammer milling, shredding, roller milling,deflakering, or refining. Dispersant reactions and fiberization can alsobe carried out at the same time by spraying the chemicals on to thefibers during fiberization processes. As FIG. 2 further shows, intreating fiberized fibers 202 c, dispersants will be sprayed onto thefiberized fibers as shown in step 204 c. The dispersant reactions areallowed to take place in a reactor with vigorous agitation/mixing. Thedispersant treatment can also be carried out in systems such as flashdryers, hammermills, conventional resin application chambers, or closedmixing tank reactors.

In yet another embodiment, fibrillated cellulose fibers in a dry formcan be used in the fiber treatment 204 d. In preparation of dryfibrillated fibers, cellulose pulp is refined using conventionalhydrapulpers, pulp refiners or deflakers. The fibrillated fibers arethen de-watered and/or dried using techniques such as flash drying andair drying. The wet or dry fibrillated fibers are then brought tocontact with desirable dispersants in a reactor. The dispersanttreatment of these embodiments can be carried out at room temperature orelevated temperatures under the atmospheric or elevated pressures. Theretention time for the treatment may vary to accommodate the process andequipment, preferably 30 seconds to 24 hours. The dosage of thedispersants is preferably in the range of about 0.001% to 20% of ovendried fibers. The reaction temperature can be up to about 250° C.,preferably below about 150° C.

As shown in FIG. 2, the treated fibers are subsequently conditioned instep 206. The treated fibers can be conditioned by techniques such asdrying, humidifying, and dispersing. After conditioning the fibers, thefibers are further processed. The fibers chemically treated with adispersant are dispersed or fibrillated. In some cases, fibrillation maynot be required. The chemically treated fibers are then incorporatedinto the manufacture of fiber cement composite materials in step 208.

The dispersants may also be applied directly in the process of makingfiber cement composite materials as will be described in greater detailbelow. Preferably, the dispersants are added to the fibers before mixingwith other ingredients. In some embodiments, the cellulose fibers usedfor preparation of chemically treated fibers with improveddispersibility are individualized cellulose fibers with partial orcomplete removals of lignin components from the fiber cell walls. Inother embodiments, the cellulose fibers used are not individualizedcellulose fibers in which the lignin components stay intact.

As an alternative to treating the fibers using the above describedmethods to impart improved dispersibility, some commercially availabletreated fluff pulp that are intended for use in the paper industry forapplications in diapers, sanitary napkins, hospital pads, and disposablefluff products can also be used as fibers in some embodiments of thepresent invention. These treated pulps used in the paper industrytypically known as treated fluff pulps typically contain debondingagents that weaken the inter-fiber and intra-fiber bonding so thatbetter fiberization of the pulp can be accomplished with lower energy.Although these treated fluff pulp products have been used exclusively inthe paper industry for the purpose of reducing fiberization energy,Applicant has found that some of these pulps can be adapted for use incertain preferred embodiments of the present invention to improve fiberdispersibility and reinforcing efficiency in a cementitious matrix.These commercial pulp products include but are not limited to:

-   -   Golden Isles EE-100 Grade 4822, 4825, 4839 from Georgia Pacific        Co. of Atlanta, Ga.;    -   NF401, NF405 and CF405 from Weyerhauser Co. of Tacoma, Wash.;    -   Rayfloc-J-MX-E from Raynoier of Jesup, Fla., and    -   Georgetown Supersoft Plus from International Paper Co. of        Tuxedo, N.Y.        Formulation of Making Fiber Reinforced Cement Materials Using        Chemically Treated Fibers with Improved Dispersibility

Several of the embodiments described herein can be encompassed by thefollowing formulation:

-   -   about 10%-80% by weight cement (hydraulic binder)    -   about 20%-80% by weight silica (aggregate)    -   about 0%-50% by weight density modifiers;    -   about 0%-10% by weight additives; and    -   about 0.5%-20%, more preferably about 4%-12%, by weight        chemically treated cellulose fibers with improved        dispersibility, or a combination of chemically treated cellulose        fibers with improved dispersibility and/or regular fibers,        and/or natural inorganic fibers, and/or synthetic fibers.

The cementitious binder is preferably Portland cement but can also be,but is not limited to, high alumina cement, lime, high phosphate cement,and ground granulated blast furnace slag cement, or mixtures thereof.The aggregate is preferably ground silica sand but can also be, but isnot limited to, amorphous silica, micro silica, silica fume,diatomaceous earth, coal combustion fly and bottom ashes, rice hull ash,blast furnace slag, granulated slag, steel slag, mineral oxides, mineralhydroxides, clays, magnasite or dolomite, metal oxides and hydroxidesand polymeric beads, or mixtures thereof.

The density modifiers can be organic and/or inorganic lightweightmaterials. The density modifiers may include plastic hollow materials,glass and ceramic materials, calcium silicate hydrates, microspheres,and volcano ashes including perlite, pumice, shirasu balloons andzeolites in expanded forms. The density modifiers can be natural orsynthetic materials. The additives can include, but are not limited to,viscosity modifiers, fire retardants, waterproofing agents, silica fume,geothermal silica, thickeners, pigments, colorants, plasticizers,forming agents, flocculents, drainage aids, wet and dry strength aids,silicone materials, aluminum powder, clay, kaolin, alumina trihydrate,mica, metakaolin, calcium carbonate, wollastonite, and polymeric resinemulsion, or mixtures of thereof.

Chemically treated cellulose fibers with improved dispersibility can beused in a variety of composite materials all having differentproportions of cementitious binders, aggregates, fibers (chemicallytreated and/or conventional), and additives to obtain optimum propertiesfor a particular application. In one embodiment, the compositeformulation contains about 0.5% to 20% chemically treated fibers withimproved dispersibility by weight. Furthermore, the chemically treatedfibers with improved dispersibility may be blended with conventionalnon-chemically treated fibers and/or synthetic polymer fibers indifferent proportions. It will be appreciated that the percentage ofchemically treated fibers with improved dispersibility may be varieddepending on the desired application and/or process. Furthermore, theproportion of the cementitious binder, aggregate, density modifiers, andadditives can also be varied to obtain optimal properties for differentapplications, such as roofing, deck, fences, paving, pipes, siding,trim, soffits, backer for tile underlayment.

In preferred embodiments of the present invention, when the buildingmaterial is to be autoclaved, a lower amount of cement in theformulation is used incorporating chemically treated, more readilydispersible cellulose fibers. The formulation for the autoclaved fibercement composite materials in one embodiment comprises:

-   -   about 20-50% by weight cement, more preferably about 35%    -   about 30-70% by weight fine ground silica, more preferably about        60%    -   about 0-50% by weight density modifiers;    -   about 0-10% by weight additives, more preferably about 5%; and    -   about 0.5-20% by weight fibers, more preferably about 4-12%        fibers, wherein some percentage, up to 100%, of the fibers is        cellulose fibers treated with dispersants to increase the        hydrophobicity and hence dispersion of the fibers.

Alternatively, for an air-cured product, a higher percentage of cementcan be used, more preferably about 60-90%. In an air-cured embodiment,the fine ground silica is not used, although silica may be used as afiller.

Preferably, for the wet processes, the chemically treated fibers withimproved dispersibility have a freeness of about 100-700 degrees ofCanadian Standard Freeness (CSF) with moisture contents of 0% to 99%based on oven dry weight measured in accordance with TAPPI method T227om-99. For dry or semi-dry processes, fiberized fibers are preferred.The cementitious binder and aggregate have surface areas of about 150 to400 m²/kg and about 300 to 450 m²/kg, respectively. The surface area forboth cement and aggregates is tested in accordance with ASTM C204-96a.

Method of Making Fiber Cement Building Materials Using ChemicallyTreated Fibers with Improved Dispersibility

A method of manufacturing a fiber reinforced composite building materialusing the formulations described constitutes another embodiment of thepresent invention. A preferred process of manufacturing a fiberreinforced cementitious composite material incorporating chemicallytreated cellulose fibers with improved dispersibility begins withtreating the cellulose fibers with one or more dispersants in which thefiber surface is made substantially hydrophobic. Preferably, thehydroxyl functional groups on the fiber surface are inhibited fromforming hydrogen bonds with other hydroxyl groups, thus substantiallyreducing the occurrence of inter-fiber bonding. In one embodiment, themethod further comprises mechanically dispersing the untreated fibers ata pre-selected consistency to separate the fibers so as to facilitatechemical treatment of the fiber surface, and fibrillating the untreatedfibers to a pre-selected freeness range. After chemically treating thefibers with a dispersant, the preferred method comprises mixing thechemically treated fibers with ingredients to form a fiber cementmixture in accordance with preferred formulations, forming the fibercement mixture into a fiber cement article of a pre-selected shape andsize, and curing the fiber cement article so as to form the fiberreinforced composite building material.

The dispersants may be applied to any of the above steps prior toforming the fiber cement mixture into a fiber cement article and curingthe fiber cement article. Preferably, the chemicals are added to thefibers first to allow enough time for the chemical reactions to takeplace before mixing the fibers with other ingredients to form the fibercement mixture. In some embodiments, however, dispersants may be addedto the fiber cement mixture while the fibers are being mixed togetherwith other ingredients. Advantageously, fibers treated with dispersantsremain substantially dispersed in a cement mixture even after themechanical mixing action stops, thereby substantially reducing theoccurrence of re-clustering or clumping of the fibers in the cementmixture. As will be described in greater detail below, the chemicallytreated fibers with improved dispersibility provide the final compositematerial with a more uniform fiber distribution and inhibit theformation of fiber clumps or clusters that are known to reduce the fiberreinforcing efficiency of the product.

Preferably, the step of mixing the chemically treated fibers withimproved dispersibility with other ingredients to form a fiber cementmixture comprises mixing the chemically treated fibers withnon-cellulose materials such as hydraulic binder, aggregate, densitymodifiers, and additives in accordance with the preferred formulationsof this invention. In some embodiments, the chemically treated fiberscan also be mixed with synthetic fibers along with other ingredients.The fabrication processes can use any of the existing technologies, suchas extrusion, molding, injection molding, casting, and Hatschek process,etc.

FIG. 3 illustrates a preferred process 300 of manufacturing a fiberreinforced cementitious composite material incorporating the chemicallytreated cellulose fibers with improved dispersibility. As FIG. 3 shows,the process begins with step 302 in which the cellulose fibers aretreated with dispersants to impart the fibers with hydrophobicity. Apre-prepared chemically treated fiber with improved dispersibility mayalso be used.

The chemically treated fibers with improved dispersibility aresubsequently processed in step 304. The fiber processing step 304typically involves fiber dispersion and fibrillations. In oneembodiment, the fibers are dispersed at a consistency of about 1% to 6%in a hydra-pulper, which also imparts some fibrillation. Furtherfibrillation can be achieved using a refiner or series of refiners. Oncedispersed, the fibers are then fibrillated to a range of about 0 to 800degrees of CSF (Canadian Standard Freeness), more preferably betweenabout 100 to 700 degrees of CSF. Dispersion and fibrillation can also beachieved by other techniques such as hammermilling, deflakering,shredding, and the like. Furthermore, use of fibers chemically treatedwith a dispersant without fibrillation is also acceptable for someproducts and processes.

As FIG. 3 shows, in step 306, the chemically treated cellulose fiberswith improved dispersibility are proportionally mixed with otheringredients to form a waterborne mixture, slurry, or paste. Preferably,the fibers are mixed with cement, silica, a density modifier and otheradditives in a well-known mixing process to form a slurry or paste. Thechemically treated fibers with improved dispersibility will more readilydisperse and distribute uniformly throughout the mix. Furthermore, thefibers will remain substantially dispersed even after the mechanicalmixing action stops, thereby reducing the occurrence of re-clustering orclumping of the fibers. In the mixer, synthetic fiber can also beblended with the chemically treated fibers with improved dispersibility.

The process 300 follows with step 308 in which the mixture may be formedinto a “green” or uncured shaped article using a number of conventionalmanufacturing techniques as would be known to one skilled in the art,such as:

Extrusion;

Hatschek sheet process;

Mazza pipe process;

Magnani process;

Injection molding;

Hand lay-up;

Molding;

Casting;

Filter pressing;

Fourdrinier forming;

Multi-wire forming;

Gap blade forming;

Gap roll/blade forming;

Bel-Roll forming;

Others.

These processes may also include a pressing or embossing operation afterthe article is formed. More preferably, no pressing is used. Theprocessing steps and parameters used to achieve the final product usinga Hatschek process are similar to what is described in Australian PatentNo. 515151:

Following step 308, the “green” or uncured shaped article is cured instep 310. The article is preferably pre-cured for up to about 80 hours,most preferably about 24 hours or less. The article is then air-curedfor approximately 30 days. More preferably, the pre-cured article isautoclaved at an elevated temperature and pressure in a steam saturatedenvironment at about 60 to 200° C. for about 3 to 30 hours, morepreferably about 24 hours or less. The time and temperature chosen forthe pre-cure and cure processes are dependent on the formulation, themanufacturing process, the process parameters, and the final form of theproduct.

Fiber Reinforced Cement Composite Materials Using Chemically TreatedFibers with Improved Dispersibility

Applications of chemically treated cellulose fibers with improveddispersibility in fiber reinforced composite materials can improve themechanical and physical properties of the final building product. Fibercement products using these chemically treated fibers have improvedfiber dispersion, improved fiber reinforcing efficiency, improvedtoughness and strain. The use of chemically treated fibers with improveddispersibility obviates the need of adding additional fibers to thecomposite material to compensate for poor fiber distribution. Thus, lessfibers are needed to achieve the same if not better physical andmechanical properties in the final product, which can result insignificant cost reductions. Other desirable characteristics of fibercement materials using the chemically treated fibers with improveddispersibility include improved water resistance and smoother surfacefinishes when extrusion, molding, or casting process is used. Moreover,long fibers that are generally more difficult to disperse than shortfibers, and thus sometimes avoided, can also be treated to provide themwith improved dispersibility. Chemically treated long fibers withimproved dispersibility can be used in the formulation to provideadditional benefits afforded by using long cellulose fibers as areinforcement agent.

The following examples demonstrate some of the desirable characteristicsthat the chemically treated fibers with improved dispersibility providein the formulations of the fiber reinforced cement composite materials.It will be appreciated that the fiber cement formulations are selectedfor comparison purposes only and that a variety of other formulationscan be used without departing from the scope of the present invention.It will also be appreciated that in addition to fiber cement products,other cementitious and non-cementitious materials such as polymeric,wood, and other materials may also use chemically treated fibers withimproved dispersibility in the formulation to improve the mechanical andphysical properties of the material. The scope of the present inventionis not limited to cementitious composite building materials nor buildingmaterials in general.

EXAMPLE 1

In this example, two types of cellulose fibers were fiberized in dryform by a hammermill. One was the debonder treated pulp of Weyerhaeuserpulp grade NF401, and the other was the control fiber, the same fiberswithout debonder treatment (Weyerhaeuser pulp grade NF416). Fiber cementcomposite specimens were fabricated using an extrusion process. Theformulation for the samples A and B was the same except different fiberswere used. The formulation contained 10% fibers (chemically treatedfibers having improved dispersion for formulation A and conventionaluntreated fiber for formulation B), 10% calcium silicate hydrate, 1.5%methylcellulose, 39.25% Portland cement and 39.25% ground silica. Theextruded samples were precured at 150° C. for 12 hours and then cured byautoclaving at 185° C. for 12 hours. The densities of Samples A and Bwere around 0.9 grams per cubic centimeter. Some key physical andmechanical properties of samples A and B are shown in Table 2.

TABLE 2 Comparison of key physical and mechanical properties of extrudedfiber cement materials using chemically treated and readily dispersiblefibers (A) and conventional untreated cellulose fibers (B) SamplesPhysical Properties A B (Control) Modulus of Rupture (MOR, MPa) 6.445.75 Z-Direction Tensile Strength (MPa) 2.33 1.81 Toughness (KJ/m³) 2.270.93

Table 2 above provides an illustrative comparison of various mechanicaland physical properties of fiber cement products made with formulationsthat incorporate chemically treated cellulose fibers to provide improveddispersibility and those that use conventional untreated fibers. Modulusof rupture (MOR), Z-direction tensile strength, and toughness weretested in accordance with ASTM (American Standard Test Method) C1185-98aentitled “Standard Test Methods for Sampling and Testing Non-AsbestosFiber-Cement Flat Sheet, Roofing and Siding Shingles, and Clapboards.”It will be appreciated by one skilled in the art that the specificvalues of particular mechanical properties will differ by varying theoven dry density.

As shown in Table 2, the MOR, Z-direction tensile strength, andtoughness are all higher for fiber cement materials made with thechemically treated fibers having improved dispersibility. In particular,toughness and strain are physical properties that are highly influencedby the degree of fiber dispersion. Therefore, the degree of fiberdispersion can be measured indirectly by comparing the strain andtoughness values of composites made with and without the chemicallytreated fibers with improved dispersibility. Fibers that are betterdispersed will result in a higher strain and toughness value per unitmass of fiber added in the final product. As shown in Table 2, thisembodiment of the invention increases the MOR by approximately 12%, theZ-direction tensile strength by approximately 28%, and toughness byapproximately 144%, when compared to the equivalent formulation madewithout chemically treated fibers with improved dispersibility. Anequivalent formulation is herein defined as one in which the preferredchemically treated cellulose fibers with improved dispersibility aredisplaced by an equivalent percentage of cellulose fibers that are nottreated with a dispersant in accordance with the embodiments of thepresent invention. Table 2 shows that fiber cement materials made withchemically treated fibers have better physical and mechanical propertiesthan fiber cement materials of equivalent formulations but made withconventional untreated fibers.

EXAMPLE 2

FIG. 4 illustrates a comparison of key mechanical and physicalproperties of extruded fiber reinforced cement composite materials madewith and without the chemically treated fibers. Sample C was preparedwith chemically treated fibers with improved dispersibility(Weyerhaeuser's grade NF405, a debonder treated fibers) while sample Dcontains regular pulp (Weyerhaeuser's grade CF416). The samples have thesame formulation except for the fibers used: 10% of treated fibers(NF405), 10% of CF416. The fibers were fiberized by hammermilling. Thesamples were prepared by extrusion and tested for MOR, Z-directiontensile strength and toughness energy in accordance with ASTM (AmericanStandard Test Method) C1185-98a entitled “Standard Test Methods forSampling and Testing Non-Asbestos Fiber-Cement Flat Sheet, Roofing andSiding Shingles, and Clapboards.” As shown in FIG. 4, extruded fiberreinforcement composite materials made with chemically treated fiberswith improved dispersibility show about 18% improvement in MOR, about 7%improvement in Z-direction tensile strength and about 200% improvementin toughness when compared to extruded fiber reinforcement compositematerials of an equivalent formulation but without the chemicallytreated fibers.

EXAMPLE 3

In this example, the formulations of samples E and F were substantiallythe same except that different fibers were used: about 9% fiber byweight (chemically treated fiber with improved dispersibility or regularuntreated fiber); about 10% calcium silicate hydrate which, in oneembodiment, is used as a density modifier, about 1.5% methylcellulosewhich, in one embodiment, is used as an additive-viscosity modifier,about 39.75% Portland cement and about 39.75% ground silica. Fibers usedin sample E were chemically treated with a surfactant emulsion, about50:50 blend of di(hydrogenated tallow) dimethyl ammonium chloride (CASnumber 61789-80-8) and alkyl-benzyl-dimethy ammonium chloride (CASnumber 61789-72-8) by the dry spraying technique. The total dosage ofthe dispersant was about 0.06% of the oven dried fiber mass. Thetreatment was done at ambient temperature before the fiberization.Fibers used in Sample F were regular untreated fibers. Specimens offiber cement composite materials were then formed using extrusion. Theextruded samples were procured at about 150° C. for about 12 hours andthen cured by autoclaving at about 185° C. for about 12 hours. Some keyphysical and mechanical properties are shown in Table 3.

TABLE 3 Comparison of key physical and mechanical properties of extrudedfiber cement materials using chemically treated fibers with improveddispersibility and regular cellulose fibers Samples Physical PropertiesE F (Control) MOR/Fiber Wt. (MPa/Kg) 0.68 0.61 Strain/Fiber Wt.(μm/m-Kg) 501 465 Toughness/Fiber Wt. (KJ/m³-Kg) 0.27 0.13

Table 3 above provides an illustrative comparison of key mechanical andphysical properties of fiber cement products that incorporate chemicallytreated cellulose fibers with improved dispersibility and those that areconventional untreated fibers. The samples were made with equivalentformulations except for the type of fibers used. Average toughness andstrain values were determined using a three point bending test inaccordance with ASTM (American Standard Test Method) C1185-98a entitled“Standard Test Methods for Sampling and Testing Non-AsbestosFiber-Cement Flat Sheet, Roofing and Siding Shingles, and Clapboards.”This embodiment of the invention increases the MOR per kilogram of fiberused by approximately 11%, the strain per kilogram of fiber used byapproximately 7%, and the toughness per kilogram of fiber used byapproximately 100%. The strain and toughness values per kilogram offiber used are indicative of the degree of fiber reinforcing efficiency.Improvements in fiber reinforcing efficiencies are typically reflectedin higher strain and toughness values per kilogram of fiber added. Thus,results in Table 3 indicate that the addition of chemically treatedfibers improved the fiber reinforcing efficiency of the material as thevalues of the strain and toughness energy per kilogram of fiber addedfor materials made with chemically treated fibers are higher than thatof materials made with an equivalent formulation without chemicallytreated fibers.

CONCLUSION

In general, it will be appreciated that preferred embodiments of thepresent invention, in particular a chemically treated cellulose fiberincorporated into a fiber cement building material, have severaladvantages over the prior art. These materials, made in accordance withthe preferred processes and formulations, have better fiber dispersionand higher fiber reinforcing efficiency, thus require less fiber dosageto attain the required physical and mechanical properties. Furthermore,improved fiber reinforcing efficiency also leads to improved physicaland mechanical properties such as higher modulus of rupture, higherZ-direction tensile strength, higher toughness, higher strain, andbetter interlaminate bonding strength. The chemically treated fiberswith improved dispersibility also improve water resistance and surfacesmoothness of the finished products, and reduce cost in fiber use.

The chemically treated fibers of the preferred embodiments of thepresent invention have reduced inter-fiber and intra-fiber hydrogenbonding and thus can be more readily dispersed in a mixture. Oncedispersed in a mixture, the chemically treated fibers tend to remaindispersed and are substantially less likely to re-cluster and form intoclumps when mechanical mixing stops. The chemically treated fibers withimproved dispersibility can be readily and uniformly distributedthroughout a cementitious matrix thus eliminating the need to add higherfiber dosage to compensate for poor fiber dispersion. In one embodiment,the use of chemically treated fibers with improved dispersibilityresults in about 5% reduction in dosage of fibers added to the buildingmaterial while still achieving the same physical and mechanicalproperties. The chemically treated fibers with improved dispersibilityalso have better dispersibility in all types of aqueous solutions.Furthermore, treating cellulose fibers with dispersants will allow bothlong and short fibers to be used in the wet and semi-wet processes ofmanufacturing fiber cement composite materials.

It will be appreciated that the fiber cement formulations are selectedfor comparison purposes only and that a variety of other formulationscan be used without departing from the scope of the present invention.In addition to fiber cement products, other materials may also usechemically treated fibers with dispersibility in the formulation toimprove the mechanical and physical properties of the material. It willalso be appreciated that several fiber treatments such as fiber sizing,biocide treatment, and fiber loading can be combined with dispersanttreatment to provide the treated fiber and the fiber cement compositematerial with even more desirable properties.

The preferred embodiments have applicability to a number of buildingproduct applications, including but not limited to roofing, paving,exterior and interior panels, decking, piping, tile backers, siding,trim, soffits, and fencing. However, it will be appreciated that thescope of the applicability of the preferred embodiments can alsoinclude, but is not limited to, non-building products and/or materialswith non-cementitious matrices. The embodiments illustrated anddescribed above are provided as examples of certain preferredembodiments of the present invention. Various changes and modificationscan be made from the embodiments presented herein by those skilled inthe art without departure from the spirit and scope of this invention.

1-8. (canceled)
 9. A building material, wherein the building materialcomprises a cementitious matrix and chemically treated fibers withimproved dispersibility incorporated in the cementitious matrix, whereinthe chemically treated fibers are treated with a dispersant to improvedispersibility.
 10. The building material of claim 9, wherein thechemically treated fibers comprise about 0.5%-20% by weight of thebuilding material.
 11. The building material of claim 9, wherein thechemically treated fibers comprise about 4%-12% by weight of thebuilding material.
 12. The building material of claim 9, wherein thechemically treated fibers increase the strain of the building materialby more than about 5% as compared to a building material made from anequivalent formulation without chemically treated fibers.
 13. Thebuilding material of claim 9, wherein the chemically treated fibersincrease the modulus of rupture of the building material by more thanabout 5% as compared to a building material made from an equivalentformulation without chemically treated fibers.
 14. The building materialof claim 9, wherein the chemically treated fibers increase theZ-direction tensile strength of the building material by more than about10% as compared to a building material made from an equivalentformulation without chemically treated fibers.
 15. The building materialof claim 9, wherein the chemically treated fibers increase the toughnessof the building material by approximately 20% as compared to a buildingmaterial made from an equivalent formulation without chemically treatedfibers.
 16. The building material of claim 9, wherein the chemicallytreated fibers reduce the fiber dosage by about 5% as compared to abuilding material made from an equivalent formulation without chemicallytreated fiber.
 17. The building material of claim 9, wherein thechemically treated fibers comprise fibers having a length-weightedaverage length of longer than about 1 mm.
 18. A method of manufacturinga building material, comprising: providing cellulose fibers; treating atleast a portion of the cellulose fibers with a dispersant to formchemically treated fibers with improved dispersibility, wherein thedispersant imparts improved fiber dispersibility in the aqueous phase;mixing the chemically treated fibers with a cementitious binder andother ingredients to form a fiber cement mixture; forming the fibercement mixture into a fiber cement article of a pre-selected shape andsize; and curing the fiber cement article so as to form a fiberreinforced composite building material.
 19. The method of claim 18,wherein treating the fibers comprises treating the cellulose fibers in asolution containing surfactants.
 20. The method of claim 18, whereintreating the fibers in solution comprises applying between about0.001%-20% of dispersants to the fibers by fiber mass.
 21. The method ofclaim 18, wherein treating the fibers comprises chemically bonding adispersant to the fiber surface in a manner such that the dispersantsubstantially blocks at least a portion of the hydroxyl groups on thefiber surface.
 22. The method of claim 18, wherein treating the fiberscomprises using a dry spray process to deposit dispersants on the fibersurface.
 23. The method of claim 18, wherein providing the fiberscomprises fiberizing the fibers, wherein the fiberization process can becarried out before, during or after the step of treating the fibers. 24.The method of claim 18, wherein providing the fibers comprisesfibrillating the fibers to a range of between about 100 to 700 degreesof Canadian Standard Freeness.
 25. The method of claim 18, whereinproviding the fibers comprises chemically removing the lignins of thefibers so as to individualize the fibers.
 26. The method of claim 18,wherein forming the fiber cement mixture into a fiber cement articlecomprises using a process selected from the group consisting ofextrusion, injection molding, molding, Hatschek, and others.
 27. Amethod of manufacturing a building material, comprising: mixing fibersthat have been chemically treated with a dispersant with a cementitiousbinder and other ingredients to form a fiber cement mixture; forming thefiber cement mixture into a fiber cement article of a pre-selected shapeand size; and curing the fiber cement article so as to form a fiberreinforced composite building material.
 28. The method of claim 27,wherein mixing fibers that have been chemically treated with adispersant comprises mixing the treated fluff pulps with a cementitiousbinder and other ingredients to form a fiber cement mixture.
 29. Abuilding material formulation used to form a building material,comprising: a hydraulic binder; an aggregate; cellulose fibers, whereinat least a portion of the fibers are at least partially treated with adispersant to form chemically treated fibers with improveddispersibility, wherein the dispersant binds hydroxyl groups on thefiber surface so as to substantially inhibit bending between hydroxylgroups of different fibers, thereby substantially reducing inter-fiberhydrogen bonding so that the chemically treated fibers can be morereadily dispersed in a mixture.
 30. The formulation of claim 29, whereinthe cellulose fibers comprise about 0.5%-20% of the formulation byweight.
 31. The formulation of claim 29, wherein about up to 100% of thecellulose fibers by weight are at least partially treated with adispersant.
 32. The formulation of claim 29, wherein the dispersanttreated cellulose fibers comprise fluff pulps treated with debonders.33. The formulation of claim 29, wherein at least a portion of thefibers are at least partially treated with a dispersant selected fromthe group consisting of polyamine compounds, cationic quaternaryaminesurfactants, alkylalkoxylsilane, alkoxylsilane, and halide organosilane,and combinations thereof.
 34. The formulation of claim 29, wherein thehydraulic binder comprises about 20%-50% cement by weight.
 35. Theformulation of claim 29, wherein the aggregate comprises about 20%-80%silica by weight.
 36. The formulation of claim 29 further comprising0%-50% additives.
 37. The formulation of claim 36, wherein the additivescomprises low density additives.
 38. The formulation of claim 29,wherein the cellulose fibers comprise individualized cellulose fibers.